The present invention relates to devices and methods for generating random bits and random bit sequences.
Random numbers, which occur in digital form as random bit sequences, are frequently required in security-related applications. It is necessary for example, with asymmetrical authentication methods, to generate and use random numbers. In particular with increasingly used RFID tags corresponding random numbers have to be generated with particularly minor hardware outlay. It is desirable here to use only digital logic circuits, which can be implemented in a manner that is favorable in respect of outlay.
In the past random number generators were used for example using analog noise sources, the signals of which are digitized. Hybrid analog/digital circuits can however only be implemented with significant outlay.
A random number generator, which has practically only digital logic circuits, is described in WO 2006/015624 A1. In this international patent application it is proposed that random phase fluctuations of ring oscillators made up of digital gates should be used. According to WO 2006/015624 A1 however only very specific ring oscillators, namely Fibonacci or Galois ring oscillators with particular characteristics, are suitable for use in a random number generator. With a circuit of such structure it is assumed that the ring oscillators cannot have fixed points. In particular for Fibonacci or Galois oscillator circuits this condition can be represented by mathematical equations, which have to be satisfied according to WO 2006/015624 A1. During corresponding implementation it should therefore be checked first whether a ring oscillator has fixed points. The selection from possible oscillator circuits is therefore disadvantageously very limited.